Iran denounced US President Donald Trump as "feeble-minded" over Monday's controversial move of the US embassy to Jerusalem, calling for resistance from the Palestinians and the international community.
"America has entered a crisis of strategic decision-making that looks at the international arena immaturely and adventurously," said parliament speaker Ali Larijani, a key establishment figure, at a conference on the Palestinian situation in Tehran.
"I believe the current US president is not capable of identifying and judging the long-term consequences of his actions," he added.
The US was due to open its new embassy in Jerusalem - known as Al-Quds in Iran - later on Monday amid widespread Palestinian anger and praise from Israelis.
"Spur-of-the-moment and uncalculated actions cannot continue in today's world. Feeblemindness is costly for statesmen and they will eventually have to pay the price," Larijani said.
Iran is a key backer of Palestinian militant groups, including Hamas, and opposition to Israel has been a central tenet of its regime since the 1979 Islamic revolution.
Larijani called for an "immediate reaction" from Palestinians, Islamic countries and the international community - including boycotts and official complaints to the UN.
The US "must not think that such actions... can remain without a response", he said.
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